For many years, ditch processes have been used to treat wastewater. One of the most successful ditch processes known is the Triple Ditch Process. The Triple Ditch Process is particularly known for its ability to perform controlled removal of nitrogen. This process and system differs from conventional activated sludge nitrification and denitrification processes in that it includes no recycle stream or external clarifier. The Triple Ditch system includes three hydraulically interconnected oxidation ditches that alternatively function as aerobic (oxic), anoxic, or quiescent reactors. The aerobic or oxic reactor performs the nitrification. The anoxic reactor performs denitrification. The quiescent reactor performs clarification. Because the flow direction through the oxidation ditches is periodically reversed, there is no need to provide for internal recycle streams or the pumping of return activated sludge. The major advantage of the Triple Ditch system is that it consistently produces a high quality effluent at a significant lower cost than conventional systems.
As noted above, the Triple Ditch Process is effective for nitrogen removal as well as the removal of BOD and suspended solids. However, in many situations it is desirable to remove another nutrient—phosphorus. It is, of course, possible to remove phosphorus from wastewater through either chemical means or biologically. There are many disadvantages to using chemicals, not the least of which is cost. Conventional biological phosphorus removal (BPR) usually entails a series of reactors, an external clarifier, and a pumping system for pumping activated sludge from the external clarifier to the front or initial reactor. See, for example, U.S. RE 32,429, the disclosure of which is expressly incorporated herein. Such conventional wastewater treatment systems require large capital expenditures and are expensive to operate and maintain. In many situations, the cost of a conventional phosphorus removal system is cost prohibited.
Therefore, there has been and continues to be a need for a cost effective and efficient biological wastewater treatment system that will remove phosphorus.